1. Field of the Invention
This invention relates to knotmeters. More particularly, it concerns rotary type knotmeters designed to detect relative motion between an underwater vehicle and the water in which it is submersed at relatively great depths.
2. Description of the Prior Art
In conducting oceanographic studies and for other reasons, there is a need for measuring the relative motion of deep-diving underwater vehicles (submersible) and the water in which they are submersed. Such relative motion may be, for example, the result of movement of the submersible through the water or, alternatively, the flow of the water past the stationary submersible. The speed values of such measurements are not large, e.g., in the range of 0.1 to 10 knots, so the measurements must be performed with high accuracy.
Historically, a variety of different types of knotmeters have been developed for use in measuring speed aboard underwater vehicles, e.g., pitot tubes, rotary vanes, drag devices, etc. The present invention employs rotary units in combination with accessory units to provide knotmeters for deep-depth submersibles that are highly accurate and reliable under submerged ambient conditions.
It is known that the form or shape of rotors for rotary type knotmeters may be varied as shown by the following U.S. patents:
Schulte, U.S. Pat. No. 2,127,847--1938 PA1 Maeder et al., U.S. Pat. No. 3,457,782--1969 PA1 Phillips, U.S. Pat. No. 3,754,441--1973.
Knotmeters employing the improvements of the present invention preferably use vaned rotors (see Schulte and Phillips), but they may use other rotor forms.
Rotary knotmeters can use a variety of means to connect the rotor to some display or recording unit. For example, such means may be mechanical linkages (see U.S. Pat. No. 1,894,211), A.C. generators (see U.S. Pat. No. 3,287,969), magnetic flux units (see U.S. Pat. Nos. 3,496,770 & 3,531,988), etc.
Knotmeters employing the improvements of the present invention preferably use Hall-effect sensors with a current-modulation, multiplexing approach to connect the knotmeter rotor to a counting/display unit. Use of Hall-effect devices, in general, as electronic control elements is well known (see U.S. Pat. No. 4,338,552), but such devices are used in unique combinations in accordance with the present invention.